README.md

1946. Largest Number After Mutating Substring

You are given a string num, which represents a large integer. You are also given a 0-indexed integer array change of length 10 that maps each digit 0-9 to another digit. More formally, digit d maps to digit change[d].

You may choose to mutate a single substring of num. To mutate a substring, replace each digit num[i] with the digit it maps to in change (i.e. replace num[i] with change[num[i]]).

Return a string representing the largest possible integer after mutating (or choosing not to) a single substring of num.

A substring is a contiguous sequence of characters within the string.

Example 1:

Input: num = "132", change = [9,8,5,0,3,6,4,2,6,8]
Output: "832"
Explanation: Replace the substring "1":
- 1 maps to change[1] = 8.
Thus, "132" becomes "832".
"832" is the largest number that can be created, so return it.

Example 2:

Input: num = "021", change = [9,4,3,5,7,2,1,9,0,6]
Output: "934"
Explanation: Replace the substring "021":
- 0 maps to change[0] = 9.
- 2 maps to change[2] = 3.
- 1 maps to change[1] = 4.
Thus, "021" becomes "934".
"934" is the largest number that can be created, so return it.

Example 3:

Input: num = "5", change = [1,4,7,5,3,2,5,6,9,4]
Output: "5"
Explanation: "5" is already the largest number that can be created, so return it.

Constraints:

• 1 <= num.length <= 105
• num consists of only digits 0-9.
• change.length == 10
• 0 <= change[d] <= 9

Solutions (Rust)

1. Solution

impl Solution {
    pub fn maximum_number(num: String, change: Vec<i32>) -> String {
        let mut digits = num.into_bytes();

        for i in 0..digits.len() {
            if digits[i] < change[(digits[i] - b'0') as usize] as u8 + b'0' {
                for j in i..digits.len() {
                    if digits[j] > change[(digits[j] - b'0') as usize] as u8 + b'0' {
                        break;
                    }

                    digits[j] = change[(digits[j] - b'0') as usize] as u8 + b'0';
                }

                break;
            }
        }

        String::from_utf8(digits).unwrap()
    }
}